Sworn Enemies are your foe you think unforgivable until the end of time. To have this kind of relationship, your Enemy Sim should be at least Relationship Level 6 to initiate the Sworn Enemy Social Event. As usual, you just need to execute actions and fill the event's progress bar. Completing this event will surely step up your mean relationship.
Generous These Sims give a bit better daily Login Rewards
Lucky These Sims occasionally give you bonus XP while at home
Mean These Sims get a bonus every now and then when being insulting with others
Competitive These Sims are a bit better at Rival Events
Good Upbringing These Sims are way better at all Events